Drug delivery by means of injections, inhalation, transdermal or swallowing pills or capsules generally results in varying drug concentrations between dosings. Many diseases would be better treated if the therapeutic drug were given so as to obtain a more or less constant drug level in the region of interest, especially if systemic drug concentrations could be maintained at or near zero thereby minimizing side effects. Implantable drug delivery devices attempt to achieve this by delivering small amounts of drug to a specific body cavity on a frequent basis. These delivery systems also are capable of protecting drugs which are unstable in vivo and that would normally require frequent dosing intervals. Implantable drug delivery devices include polymeric implants, implantable osmotic pump systems, and micro-pumps.
Polymeric implants, used extensively in controlled drug delivery systems, include non-degradable polymeric reservoirs and matrices, and biodegradable polymeric devices. In both cases the drug is released by dissolution into the polymer and then diffusion through the walls of the polymeric device. The release kinetics of drugs from such systems depends on both the solubility and diffusion coefficient of the drug in the polymer, the drug load, and, in the case of the biodegradable systems, the in vivo degradation rate of the polymer. Examples of polymeric implants include simple cylindrical reservoirs of medication surrounded by a polymeric membrane and homogeneous dispersions of drug particles throughout a solid matrix of non-degradable polymers. Biodegradable polymeric devices are formed by physically entrapping drug molecules into matrices or microspheres. These polymers dissolve when implanted or injected and release drugs.
Another method for controlled prolonged delivery of a drug is the use of an implantable osmotic pump. An osmotic pump is generally in a capsule form having permeable walls that allow the passing of water into the interior of the capsule containing a drug agent. The absorption of water by the water-attracting drug composition within the capsule reservoir creates an osmotic pressure within the capsule to push the drug out of the capsule to the treatment site.
Implantable micro-pumps for drug delivery applications usually include a permeable membrane for controlled diffusion of a drug into the body from a suitable reservoir. Such devices are limited in application primarily since the rate at which the drug is delivered to the body is completely dependent upon the rate of diffusion through the permeable membrane. With these devices the rate of drug delivery to the body may be affected by differing conditions within the body. In addition, such systems make no provision for the adjustment of the rate or time interval for drug delivery, nor can the delivery rate be easily varied.
Although polymeric implants, osmotic pumps and micro-pumps may provide a relatively steady rate of drug release, some drugs are more effective given in intervals. Implantable infusion pumps can be programmed to deliver drugs at very precise dosages and delivery rates. These pumps may have a feedback device that controls drug delivery according to need. With the current development of electronics and miniaturization of pumps and sensors, various vital signs can be monitored leading to feedback systems such as for monitoring blood glucose levels and delivering insulin when needed. The size of the pump depends on the amount of drug and the intended length of treatment. A barrier in feedback technology in using an implantable sensor is the problem of body proteins causing reduced sensitivity of the sensors, compromising the reliability of the sensor input.
There are many existing examples of implantable medical device applications. Implantable insulin pump technology has been developed with a goal of simulating the normal function of the pancreas by using glucose sensors and the predictive mathematical models. The sensors would assess the level of glucose in the blood and pass the information to a control algorithm used in a microprocessor chip for causing appropriate action by the pump. Such a device delivers a dose of insulin through a catheter into a patient's abdominal cavity. According to one manufacturer a disk-shaped pump weight of about 5 to 8 ounces when filled can hold an insulin supply adequate for several months and can be refilled with a syringe injection across abdominal tissue with battery life lasting about eight to 13 years. This delivery system keeps the liver from secreting excess glucose (blood sugar) into the bloodstream. Current pump technology difficulties include blockage of the catheter, infection at the implantation site, as well as accidentally injecting insulin refills into patient's abdomen instead of the pump reservoir. A typical reservoir in an implantable pump is to be refilled every three months.
For pain relief, drug delivery devices include the SynchroMed, an externally programmable implantable device for the administration of morphine sulfate to treat chronic pain, and the AlgoMed, designed to treat intractable pain in cancer patients. The AlgoMed device includes a drug reservoir implanted just under the skin of the abdomen, and a small catheter that delivers medicine to the spinal cord.
The treatment of glaucoma presents several strong challenges to drug delivery implant technology due to the sensitivity of the eye which therefore requires more frequent and precise dosing of medication while the small anatomical space limits the size of an ocular implant device. The surface of the eye is a significant physical barrier to medications that target intraocular treatment sites. Topical eye drops must be able to permeate through the modified mucosal membrane that covers the cornea. Only a very small percentage (−5%) of the eye drops actually reach the intraocular space. While drugs that are released rapidly produce a relatively rapid and high concentration in the body, followed by a sharp decline, it is preferable to have controlled-release systems deliver a drug at a slower rate for a longer period without manual application by patients. In many glaucoma treatments, two drugs are used; a first drug for reducing internal pressure inside the eye and a second drug for reducing side effects. It is, therefore, desirable to have a compact drug delivery device that can dispense two drugs with separate dispensing controls.
To improve the reliability and safety of an implantable drug delivery pump device, it is desirable to have a pump with a catheter with positive closing and a failsafe refilling process eliminating any possibility of injecting drug into a body cavity during the refilling process, an automatic notification feature to alert the patient of the need to take timely refilling action, as well as a process for verifying the performance of the pump. Preferably all of these desirable features can be achieved in an implantable drug delivery pump device using an implantable battery and without using an external controller.
To maintain a more constant rate of dispensing drug dosages, it is desirable to have an implant pump capable of precisely delivering a small amount of drug volume in the nano-liter range at each step of piston movement. It is desirable to infuse such minute dosages at time intervals appropriate for sustaining drug efficacy while avoiding side effects. And it is desirable to have an automated refilling process to prevent the injection of drug outside the implant pump into body tissues while refilling the pump.
The following references describe implantable devices.
U.S. Pat. No. 6,497,699 by Ludvig, et al. describes a miniature apparatus for the treatment of brain disorders. The apparatus is a combination of electronic and pharmacological devices placed and powered entirely within the human body. A neuroprosthesis monitors the electrical activity of a dysfunctioning brain area and delivers drug molecules into the problem area. The apparatus includes a refillable drug pump; a recording electrode for outputting an electrical signal characteristic of an electrical activity of the brain; and a microcontroller to control the dispensing of the drug based on the electrical signal. The timing and duration of the drug deliveries are determined by the feedback of the brain's own electrical activity. The invention describes an application of an implantable pump having multiple dispensing outlets for targeting different problem areas. However, no specific pump design is mentioned.
U.S. Pat. No. 5,832,932 by Elsberry, et al. discloses techniques and apparatus for infusing drugs into the brain to treat movement disorders. The invention employs an implantable pump and a catheter for infusing therapeutic dosages of the one or more drugs into the brain at treatment sites. A sensor for detecting the extent of the abnormal motor behavior may be used in combination with the implantable pump and catheter. The therapeutic dosage is adjusted according to signal input of the sensor to decrease the abnormal motor behavior. According to the patent the method is applicable to treat the symptoms of hypokinetic disorders, such as Parkinson's disease, and hyperkinetic disorders, such as Amyotrophic Lateral Sclerosis, Huntington's Disease, Ballism or Dystonia. The application of drug delivery device for treating movement disorder by brain infusion and the method of using a sensor for motion feedback for adjusting drug dosage in an implantable pump device are incorporated by reference.
For ophthalmic applications, U.S. Pat. No. 6,976,982 by Santini, Jr., et al. and U.S. Pat. No. 7,455,667 by Uhland, et al. provide a flexible microchip drug delivery device that attaches to the curved surface of an eyeball. The ophthalmic microchip device is in the form of an array of drug-containing microchips that are attached to a flexible supporting layer conforming to the backside surface of an eye. Release of the contents of each microchip reservoir is controlled by diffusion through, or disintegration of, the reservoir cap. The reservoir cap can be an anode made of thin film gold in electrical communication with a cathode in the device. When an electric potential of approximately 1 volt is applied the reservoir cap is oxidized to facilitate its disintegration, exposing the reservoir contents to the surrounding fluid. A microprocessor is preprogrammed to release drug from specific reservoirs by directing power from a battery to specific reservoir caps. Once released, the drug is in contact with the surface of the eye and diffuses into the eye. The reservoir activation can also be conducted wirelessly by telemetry with electromagnetic or optical means. An optical means can use an ophthalmic laser to activate LED receivers in the device. However, a potential problem with these devices is that the dissolved cap material is not removed and may even “re-solidify” when the power for dissolving the cap material is off.
The invention of U.S. Pat. No. 7,181,287 by Greenberg deals with retina stimulation by electrodes or by drug to enable vision in blind patients or treatment of a chronic condition. Specifically it is directed to an implantable device to enable delivery of drugs to the retina for stimulating the retina. The drug delivery device is secured by a tack to the retina at a desired location without damaging the retina and it is out of the field of vision from the lens to the retina. The device may be a passive osmosis type in the form of a hollow flexible polymeric pillow containing drug for slow release to deliver drugs through multiple orifices to the desired treatment sites. The device may also be an active pump type receiving drug from a reservoir transferred by a pressure development device through a tube with the flow rate controlled by a micro-valve. The micro-valve, the pressure development device and the reservoir are attached to the sclera outside the eye under the conjunctiva for ease of refilling of the reservoir. Also by the same author, U.S. Pat. No. 7,483,750 specifically discloses preferred position of a retinal device and the connection between a device reservoir and the retinal device for avoiding damaging to the retina. The retinal implant is implanted subretinally at the back of the eye near the fovea between the photoreceptor cell layer and the retinal pigment epithelium. The conduit connects the retinal implant with the drug reservoir transretinally through retinal incision and the vitreous cavity. The preferred retina incision is at a location near the front of the eye where there is no retina to avoiding damage to the nutrient rich choroid and disruption of the blood supply to the retina. These two patents provide applications and suitable location of a drug delivery device for treatments of chronic eye conditions and indicate the feasibility of separating the small-size drug pillow positioned inside the retina layer from the larger size pump body positioned outside the eye. However, the patents do not address the mechanism of dispensing the drug in controlled manner. The use of an implantable pump for treating retinal diseases is incorporated by reference.
U.S. Pat. No. 6,077,299 by Adelberg, et al. deals with a non-invasively adjustable valve implant for the drainage of aqueous humor in glaucoma. The implant valve is a rotor-type device with the valve opening controllable by a magnetic field through an external instrument. The glaucoma valve of the invention overcomes the excess absorption problem of a newly implanted pump in a treatment area, where the aqueous humor is readily absorbed into the Tenon's tissue overlying the implant. Excess absorption can cause the pressure within the eye to fall to an unacceptably low level damaging eyesight. A higher pressure set-point can be made in the implant valve for the first few days after surgery to minimize the risk of the complications. The implant valve can also be adjusted to compensate for changes due to partial occlusion of the inlet tube by particulate matter and infiltration by body tissue. However, the valve implant of this invention is not a pump for dispensing drug. Nevertheless, the patent shows that non-invasive adjustability is required for an implant device.
For ocular drug delivery, U.S. Pat. No. 3,618,604 by Ness discloses a drug-dispensing ocular insert to deliver drug to the eye over a prolonged period of time. The ocular insert is comprised of either a flexible body of polymeric material or a sealed container having membrane walls insoluble in tear liquid and having an imperforate surface. The drug contained in the insert is diffused at a controlled rate through the polymeric material or the membrane walls to the eye in a therapeutically effective amount. The ocular insert is to be placed in the cul-de-sac of the conjunctiva between the sclera of the eyeball and the lower lid. The inserts depend on osmotic pressure difference to control drug delivery and they are not personalized for individual needs. Their diffusion rates are not changeable once installed. An implant pump with programmable timed release is desirable and to enable more varied applications.
U.S. Pat. No. 7,377,907 by Shekalim provides an insulin pump that supplies insulin in a pre-pressurized chamber through a flow control valve. Precise metering is achieved by a piezoelectric actuator. The insulin in the chamber is pressurized and dispensed by a piston, which is driven by a biased spring. The device also includes a pressure regulator, a removable cartridge unit containing a pre-pressurized fluid reservoir, and an electronic package for the programming of basal rates. Nevertheless, patients with a portal device are at risk for trans-cutaneous infections.
To ensure positive closure at the dispensing opening, U.S. Pat. No. 5,997,527 by Gumucio, et al. provides a drug delivery capsule device comprising an osmotic-agent chamber having a semi permeable membrane wall, a drug chamber attached with a slit valve, and a moveable piston separating the two chambers. Under an osmotic pressure created in the osmotic chamber, the piston pushes drug through the slit valve. Being exposed to the body tissue environment the permeable membrane wall of the osmotic chamber wall allows body fluid to pass into the capsule by osmosis to create an osmotic pressure to drive the piston. The osmotic capsule of this invention lacks active control for ensuring positive closing of the slit valve. In operation, the osmotic pressure varies with the movement of the piston and the remaining quantity of the drug in the drug chamber. At one end, an excessive osmotic pressure can keep the slit valve at open state with continuous dispensing with a possibility of over-dosing. At the other end, an insufficient osmotic pressure cannot drive the piston to open the slit valve resulting in no drug being dispensed. This unreliable drug delivery due to lack of active control can cause discomfort and adverse side effects in the patient.
On the use of two fluidic drug chambers, U.S. Pat. No. 5,607,418 by Arzbaecher provides an implantable drug delivery device having a deformable dispensing chamber within a deformable reservoir chamber. In this configuration, the dispensing flow rate of the dispensing chamber is designed to be greater than the refilling flow rate from the reservoir chamber and that the reservoir chamber automatically refills the dispensing chamber following discharge of a dispensing portion of the fluidic drug. Because the dispensing rate is greater than the refilling rate across the internal valve between the two deformable chambers, a partial vacuum may be created in the two chambers resulting in a poorly controlled dispensing rate or interruption of the dispensing flow to the treatment site. The deformable dispensing chamber within a deformable reservoir chamber cannot ensure that the drug flow rate in and out of the dispensing chamber and the reservoir chamber are equal.
U.S. Pat. No. 4,883,467 by Franetzki addresses the problem of gas bubbles in pumping medication fluid in a conventional implantable medication device using a reciprocating piston pump wherein the medication reservoir is typically under atmospheric pressure between 0.5 and 1.0 bar. Gas bubbles may be generated in pumping the medication fluid at below ambient pressure or during refilling of the medication reservoir. In the reciprocating motion in the pump chamber a gas bubble would be merely compressed and decompressed without being transported out of the device, making the infusion performance of the device unreliable. This under-pressure pumping is less a problem in larger pumps having a displacement volume greater than 10 microliters. But the existence of dead space in the pump chamber of a small pump is compounded because the size of the dead space may be comparable to the size of the displacement volume of the piston. In this case, pumping medication containing gas bubbles may become impossible particularly at the lower limit of the under-pressure (0.5 bar). This patent provides an implantable medication device using a magnetized reciprocating piston and a magnetic check valve for pumping medication fluid containing gas bubbles to achieve a satisfactory infusion rate such that the patient would receive medication without interruption by the gas bubbles. The piston contains a magnetic material which can be driven by a magnetic means to move the piston forward for dispensing and a separate magnetic means for moving the piston backward. The magnetic check valve is normally biased to block fluid flow.
Addressing the problem of gas bubble formation, U.S. Pat. No. 7,201,746 by Olsen provides an implantable therapeutic substance delivery device having a piston pump with an anti-cavitation. The device has an inlet chamber and a pumping chamber. In the pumping chamber a piston having a permanent magnet is driven by the magnetic fields created by two separate inductive coils which impart a reciprocating motion to the piston to pump fluid from the pumping chamber into an outlet. In such a pump chamber the backflow of fluid from the inlet chamber can decrease pressure in the pumping chamber causing gasses to come out of solution when the pumping chamber is being filled with the fluid. The invention provides an anti-cavitation valve that is configured to open when the therapeutic substance inlet pressure exceeds the inlet chamber pressure and to close when the inlet chamber pressure exceeds the therapeutic substance inlet pressure. The objective of the anti-cavitation valve is to prevent the pumping chamber pressure from decreasing below a predetermined low pressure level during piston retraction and to enable more complete filling of the pumping chanter when the piston is retracted.
Both U.S. Pat. Nos. 4,883,467 and 7,201,746 utilize a magnetized piston driven by magnetic forces and attempt to suppress gas bubble formation by using biased valve mechanisms to increase the pressure in their pump chambers. However, without positive mechanical control of the piston, the piston movement under the magnetic forces depends on the pressure level in the pump chamber, which may vary in operation. Also, the compressed gas bubbles inside the pump chamber may expand when released at the device exit at the treatment site. Furthermore, these device configurations inherently entrap gas pockets and allow for the existence of dead space which is a major source of the pumping problem.
US Patent Application 20080287874 by Elmouelhi controls the dead volume of a piston pump by using an adjustment screw. The infusion pump device is of a reciprocating magnetized piston-type driven by solenoid coils. Typical manufacturing tolerances in the production of the pump components may result in unwanted dead space in the pumping chamber. The dead space includes space that the piston does not reach at the limit of its forward movement that leads to trapped air bubbles not displaced during the pumping strokes. the pumping volume of the piston may not be accurate as the piston movement may result in the compression of the air bubbles rather than displacement of the fluid. The invention solves the problem by adjusting the end position of the piston's forward stroke with an adjustment screw allowing for selective elimination of the dead volume and precise adjustment of the fluid pumped. Similarly US Patent Application 20080269682 by Kavazov et al. address the reservoir air bubble problems of a magnetized reciprocating piston pump by modifying the geometry of the plunger or the reservoir of the pump device. In various embodiments of the invention, a reservoir, a plunger head which moves within the reservoir, or both the reservoir and the plunger head are shaped to form a bubble trap region for trapping air bubbles so as to limit the presence of air bubbles in a fluidic medium expelled from the reservoir. Both of these patents recognize the existence of dead volume due to the structure of its piston pump device and attempt to minimize the air bubble problems. However, a piston pump that eliminates dead volume such that no air bubble problems exist would be preferable.
On refilling, U.S. Pat. No. 7,347,854 by Shelton, et al. relates to a process of refilling an implantable drug delivery device. The controller in accordance with this invention is programmed to determine the volume of the old drug remaining in the reservoir. The controller then monitors the subsequent delivery of the old drug to the patient to determine when the remaining old drug has been cleared from the device. Accordingly, the controller adopts a new dispensing profile for the drug refilled into the reservoir. The process as described in this patent is limited to the general practice of adding new drug after using up the original drug in the reservoir. No specific refill steps such as retracting a piston, closing a dispensing tip and using a passive syringe are addressed. In fact, a programmable pump allows changing the dispensing profile at any time depending on the need of a patient prior to using up the existing drug in the reservoir.
An implantable drug delivery pump of U.S. Pat. No. 6,283,949 by Roorda discloses a method of dispensing drug at a controllable rate from a reservoir. The pump includes a reservoir, a dispensing chamber, a compressible dispensing tube attached to the dispensing chamber, and a rotating-arm actuator for applying a compressive force onto the dispensing tube to deliver the drug through a catheter. The rotating-arm actuator allows additional drug drawn into the dispensing tube from the reservoir, which can be refilled. A one-way intake valve is used and the reservoir can be refilled through a septum. In this method, rotational actuator compressive force is used and the reservoir is limited to a circular configuration to accommodate the rotating arm. The patent does not address failsafe requirements for refilling a pump reservoir.
U.S. Pat. No. 4,784,646 by Feingold provides a subcutaneous delivery device for injecting drug to a local destination. The subcutaneous delivery device is mainly a catheter having a self-sealing port at the input end attached with an internal magnet and a valve at the output end. The catheter device further includes a corresponding external magnet, separated from the internal magnet by the skin, as a locator for magnetically adapting to the internal magnet. The attraction between the two magnets, which are annular magnets of opposite polarities, can facilitate positioning and stabilizing a syringe needle during injection. However, the syringe needle may still be inserted at wrong location and the drug in the syringe be injected by pressing the plunger of the syringe, therefore, causing damage to body tissues. Furthermore, the valve at the dispensing end of the device cannot be positively controlled for closing as the internal pressure in the device may exceed the self-closing pressure of the valve.
U.S. Pat. No. 7,044,932 by Borchard, et al. provides an access template for locating the refill septum of an implant drug pump. The needle insertion occurs without using radiological instruments for guidance. The access template comprises a denial surface, an access port, and template labeling. The denial surface has a periphery with a location diameter and an alignment feature. The denial surface is configured to prevent penetration through a dermal layer into the implantable drug pump. Using labels of the same color in both the template labeling and the needle labeling provides a means for ensuring the proper drug being administered but the system is not failsafe as negligence in matching colors may occur.
To locate an implantable pump for the purpose of refilling, U.S. Pat. No. 7,191,011 by Cantlon discloses the use of a port with light emitters. The light emitters can be arranged in various geometric forms and colors. Also disclosed are energy emitters such as light emitting diodes, edge emitting diodes, or VCSELs, and sonic emitters. The concepts as disclosed are not applicable for situations where light or sonic waves cannot be detected such as under the skull. Furthermore, U.S. Pat. No. 7,356,382 by Vanderveen describes a system and method for verifying that a particular fluid supply is connected to an infusion pump by means of an operator-induced pressure change. An upstream pressure sensor coupled to a fluid supply conduit provides pressure signals to a processor. In a verification mode, the processor receives the pressure sensor signals in comparison with an operator-induced pressure change in the conduit to verify that the particular fluid supply is connected to the infusion pump. The processor also prompts the operator to confirm the pressure change if the pressure change signal is not detected within a predetermined time period. However, use of an operator-induced pressure change is not fail-proof. An operator may enter incorrect pressure values or connect the wrong drug supply with a correct pressure signal. A fail-proof system is needed to eliminate a possibility of operator errors.
U.S. Pat. No. 7,212,863 by Strandberg uses a test magnet in a specified time period for external activation of an implantable medical device, which can be externally programmed within the specified time period. When the magnet is taken away the implant device returns to the normal mode of operation. The use of test magnets is a simple means of external control of the operation of an implant device without involving a complex programmable external controller. The method of using an external test magnet for activating an internal device is incorporated by reference.
On programming features, U.S. Pat. No. 6,381,496 by Meadows, et al. provides context switching features for changing the operational parameters of an implantable device. These features enable a patient to change the current set of operational parameters to another set of operational parameters. The ability to change the current operational parameter set (OPS) is accomplished by including memory circuitry within the implant device wherein a plurality of OPS's are stored. An OPS setting can be manually activated and transmitted to the implant device to replace the current OPS. The patent provides programmable features for changing operational parameter settings, but it does not address refill steps and failsafe features.
U.S. Pat. No. 5,814,015 by Gargano, et al. uses a software warning as a failsafe measure for preventing the infusion of a wrong drug. A processor driven syringe pump for two syringes in a housing unit is suspended from an IV pole. Its software provides a number of feedback warnings and alarms. The syringe plunger is driven into the syringe barrel by a motor operated by a failsafe feature against a short circuit in a drive circuit element feeding continuous current into the pump motor. A pusher assembly for the syringe includes a split nut that can be rotated and released to enable proper positioning of the syringe. The two pumps are jointly programmable and operable to allow the automatic stopping of a first pump and starting of a second pump for extended sequential infusion. Although the warnings and the failsafe feature are provided by the software against a short circuit they do not guarantee prevention of the infusion of the wrong drug. An ideal failsafe feature should provide a means for automatically preventing the refilling of a drug chamber with an incorrect drug.
On drive means for imparting a piston or plunger motion a pump device, a piezoelectric motor driven by electric pulses can be used. U.S. Pat. No. 6,940,209 by Henderson provides a piezoelectric lead screw motor for driving an assembly that contains a threaded shaft and a threaded nut. Subjecting the threaded nut to piezoelectric vibrations causes the threaded shaft to simultaneously rotate and translate in the axial direction. A drive product based on the concept called Squiggle motor has been commercialized. The SQUIGGLE SQ-306 model is 10 mm in length and 4 mm in diameter, and achieves precision levels in the micron range. The motor's power efficiency enables long battery life, which is a critical factor for implanted medical devices. Its motor driver board including ASIC, resonant inductors, Boost circuit and FWD diode can be packaged into 10 mm×10 mm×1.5 mm size. The use of commercially available SQUIGGLE motor is incorporated by reference.
US Patent Application 20080108862 by Jordan; Alain et al. describes an implantable device comprising a stepper motor for driving with an oscillator and an external controller for monitoring and correction of the performance of the device by passive telemetry. The displacement of the actuator is proportional to the number of pulses given to the motor coils. The method requires the use of an antenna coil coupled with a RF-to-DC converter to convert received RF energy to a DC voltage. However, the antenna coil and the converter add to the size of an implantable pump. The use of stepper motor as a drive means is incorporated by reference.
Alternatively, a piston or a plunger in a pump device can be driven by induction coils. U.S. Pat. No. 7,331,654 by Horsnell, et al. provides a solenoid valve mechanism using induction coils for controlling the flow of fluid through the valve. The valve mechanism includes a plunger member for axial reciprocation within a tubular member supporting an electric coil for generating a magnetic field when an electric current passes through the coil. The plunger is made of an electromagnetic material and can be magnetized by a magnetic field. The reciprocating motion of the plunger is adapted to open or close a nozzle orifice for injecting fluid drops on demand, such as on ink jet printer applications. The patent provides an example of using induction coils for driving plunger movements for dispensing fluid. The use of induction coils as a drive means is incorporated by reference.
With the limitations of the current implantable infusion pump technology, it is an objective of the present invention to prevent clogging at the catheter exit and the creation of a paritla vacuum inside the delivery device. It is an objective to provide a failsafe refilling process and an automatic notification feature for the patient to take timely action. Additionally, it is another objective to provide a drug chamber configuration to enable dispensing of minute precise drug volumes at high frequency or at a continuous mode. It is another objective to provide a compact drug delivery device to dispense two drugs without mis-matching during the refilling process.